Method for reducing fluid loss from oilfield cement slurries using vinyl grafted wattle tannin

ABSTRACT

A process for forming an oil well cement composition comprising: mixing cement and a vinyl grafted wattle tannin fluid loss additive, the vinyl grafted wattle tannin comprising a wattle tannin grafted with at least one vinyl monomer selected from the group consisting of: 2-acrylamido-2-methylpropanesulfonic acid and acrylamide, wherein the wattle tannin is present in an amount of between about 0.05 to about 14 weight percent based on actives, the 2-acrylamido-2-methylpropanesulfonic acid is present in an amount of between about 68 to about 99.95 percent, and acrylamide is present in an amount of between about 0 to about 18 percent, to form a cement blend; and mixing the cement blend with water.

This is a continuation-in-part of application Ser. No. 07/598,059, filedOct. 15, 1990 now U.S. Pat. No. 5,134,215.

The present invention provides an improved method for reducing fluidloss from oilfield cement slurries using vinyl grafted wattle tannin andtannin derivatives. The vinyl grafted wattle tannin comprises a wattletannin grafted with at least one vinyl monomer selected from the groupconsisting of: 2-acrylamido-2-methylpropanesulfonic acid and acrylamide.

BACKGROUND OF THE INVENTION

Certain polymer compositions have long been recognized by those skilledin the art as additives useful in reducing fluid loss. Thesecompositions are commonly referred to as "fluid loss additives".

Fluid loss additives are typically used in cementing oil wells. Foroilfield cementing operations to be successful additives which reducefluid loss are required to be added to the cement. Such additives willbe used in well operations where the bottom hole circulating temperature(BHCT) may range from 80°-400° F., substantial salt concentrations maybe present, and cement slurry retardation and viscosity are criticalaspects as the same affect pumpability and compressive strength.

Some examples of fluid loss additives are set forth in the followingU.S. Pat. Nos.: 4,678,591 (Giddings et al.), issued Jul. 7, 1987,4,515,635 (Rao et al.), issued May 7, 1985, and 4,676,317, (Fry et al.),issued Jun. 30, 1987.

The Rao patent discloses typical polymers used as fluid loss additives,e.g., copolymers of N,N-dimethylacrylamide and2-acrylamido-2-methylpropanesulfonic acid having molar ratios of between1:4 and 4:1, respectively, and an average molecular weight of betweenabout 75,000 and about 300,000. Other fluid loss additives disclosed inthe Rao patent are: a copolymer of a sulfonic acid modified acrylamideand a polyvinyl crosslinking agent, and a hydrolyzed copolymer ofacrylamide and 2-acrylamido-2-methylpropanesulfonic acid (AMPS).

Giddings et al. disclose a terpolymer composition for aqueous drillingfluids comprising sodium AMPS (72-3.8%), N,N-dimethylacrylamide(13.5-0.7%), and acrylonitrile (9.5-0.5%). This terpolymer compositionalso contains lignin, modified lignin, brown coal, or modified browncoal in an amount ranging from between 5-95% with the lignin, modifiedlignin, brown coal, or modified brown coal having been present duringthe polymerization of the water-soluble polymer. It has a molecularweight in the range of 10,000-500,000. The lignin, modified lignin,brown coal, or modified brown coal is from the group consisting oflignites, sulfonated lignites, lignins, leonardites, lignosulfonates,alkali metal humic acid salts, humic acids, and sulfonated humic acids.

Another fluid loss additive disclosed in Giddings et al. is RESINEX, asulfonated lignite complexed with sulfonated phenolic resin.

The Fry patent discloses a graft polymer fluid loss additive comprisinga backbone of at least one member selected from the group consisting oflignin, lignite, and their salts, and a grafted pendant group of atleast one member selected from the group consisting of AMPS,acrylonitrile, N.N-dimethylacrylamide, acrylic acid,N,N-dialkylaminoethyl methacrylate, wherein the alkyl radical comprisesat least one member selected from the group consisting of methyl, ethyland propyl radicals.

The petroleum industry prefers a fluid loss additive that has as littleeffect on compressive strength, set time, viscosity, and thickening timeas possible; a fluid loss additive that is salt tolerant (i.e., does notexhibit substantial loss of effectiveness in the presence of salt); anda fluid loss additive that is chemically stable during cementingoperations. Furthermore, fluid loss additives should be compatible withas many other additives and environmental conditions as possible, shouldbe soluble in cement slurries at normal ambient temperatures encounteredin oil well cementing operations, and should continue to provide fluidloss characteristics over broad temperature and cement pH ranges.

The present inventors have discovered that fluid loss may be reduced inoilfield cement slurries by using novel vinyl grafted wattle tanninfluid loss additives which encompass much of the aforementioned desiredcharacteristics.

U.S. Pat. No. 4,579,927 (Patel et al.), which issued on Apr. 1, 1986,discloses a water soluble polymer, i.e., a polymer consisting of a minorportion of tannin derived monomers and one or more acrylic monomers,which exhibits thermal stability characteristics when used as anadditive in aqueous drilling fluids. These water soluble polymers arepurported to control the viscosity, gel strength and fluid losscharacteristics of an aqueous drilling fluid when exposed to downholetemperatures in excess of 300° F. The water soluble polymers aretypically copolymers of flavanoid tannins and ethylenically unsaturatedcomonomers. The polymers are formed by free radical initiatedpolymerization.

Some examples of the water soluble polymer are (1) 20% sulfonatedquebracho tannin, 70% AMPS and 10% acrylamide, and (2) 11% sulfonatedquebracho tannin, 54% acrylamide, 21% AMPS, and 13% maleic acid. Theincorporation of AMPS into the polymer improves the rheology and fluidloss of the drilling fluid. Common sources of flavanoid tannins includeextracts of quebracho, wattle, mimosa, mangrove, chestnut, gambier andcutch. In certain applications the flavanoid tannins are sulfonated toenhance solubility characteristics.

All the examples in Patel et al. are directed to sulfonated quebrachotannins. In comparative studies conducted by the present inventors, itwas apparent that the novel vinyl grafted wattle tannins of the presentinvention clearly out performed the quebracho tannins as fluid lossadditives in cement slurries. Tannin and acrylamide retard the set timeof cement slurries. According to the present invention, the amount oftannin and acrylamide was adjusted to be useful for fluid loss but notoverly retard the set time. The data generated by the present inventorsdemonstrate that the grafted quebracho tannin examples set forth in thePatel et al. patent would not be useful as fluid loss additives foroilfield cementing.

It is noted that the vinyl grafted quebracho tannins of Patel et al.were prepared primarily for use as fluid loss additives in drillingfluids or muds. The application of such fluid loss additives tohydraulic cement, although briefly referred to in Patel et al., wasapparently not attempted. Had Patel et al. tried to use the fluid lossadditives formed in accordance with the teachings thereof in oilfieldcement slurries, it is believed those additives would not have exhibitedacceptable fluid loss properties.

The present inventors have discovered through extensive experimentationand comparative analysis that wattle tannin, not quebracho tannin,grafted to selected vinyl monomers performed extremely well as fluidloss additives in cement slurries. Furthermore, when oilfield cementslurries were treated with the vinyl grafted wattle tannins of thepresent invention they exhibited improved fluid loss control over thecorresponding vinyl polymers alone and vinyl monomers grafted withlignite.

The development of a vinyl grafted wattle tannin fluid loss additivethat was repeatable and which exhibited satisfactory fluid lossperformance characteristics was extremely difficult. Many graftreactions with tannin resins were performed by the inventors. Someresins were made by reacting tannin with formalin under acid and baseconditions. Some resins were made with epichlorohydrin andglutaraldehyde under appropriate conditions. Acceptable grafts were onlyrealized when the tannin level was cut back from 20%. The level ofinitiator required for grafting was proportional to the tannin content.Only when the tannin level was reduced to 14% and below did the graftsbecome repeatable and the performance improved.

Additional advantages of the present invention shall become apparent asdescribed below.

SUMMARY OF THE INVENTION

A vinyl grafted wattle tannin fluid loss additive comprising a wattletannin grafted with at least one vinyl monomer selected from the groupconsisting of: 2-acrylamido-2-methylpropanesulfonic acid and acrylamide.The wattle tannin is preferably present in an amount of between about0.05 to about 14 weight percent based on actives. The2-acrylamido-2-methylpropanesulfonic acid is preferably present in anamount of between about 68 to about 99.95 percent and the acrylamide ispreferably present in an amount of between about 0 to about 18 percent.

Optionally, wattle tannin may be derivatized prior to grafting with thevinyl monomers. The wattle tannin is preferably modified with at leastone compound selected from the group consisting of: epichlorohydrin,formaldehyde, and glutaraldehyde.

The vinyl grafted wattle tannin may also include a crosslinking agent toincrease branching and molecular weight. The preferred crosslinkingagent is methylenebisacrylamide (MBA).

Furthermore, the present invention includes a process for forming an oilwell cement composition comprising: mixing cement and a vinyl graftedwattle tannin fluid loss additive to form a cement blend; and mixing thecement blend with water.

The present invention may also include many additional features whichshall be further described below.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The vinyl grafted wattle tannin fluid loss additive according to thepresent invention comprises a wattle tannin grafted with at least onevinyl monomer selected from the group consisting of:2-acrylamido-2-methylpropanesulfonic acid (AMPS) and acrylamide (Acam),wherein the wattle tannin is present in an amount of between about 0.05to about 14 weight percent based on the resultant polymer,2-acrylamido-2-methylpropanesulfonic acid is present in an amount ofbetween about 68 to about 99.95 percent, and acrylamide is present in anamount of between about 0 to about 18 percent.

Tannin is acidic and easily forms relatively stable free radicals.Wattle tannin is condensed by reacting the tannin with epichlorohydrin,formaldehyde, or glutaraldehyde, and also self-condenses under alkalineconditions.

Improvements in the graft were realized when the tannin level was cutback from 20% based on the polymer. When the tannin level was reduced to14% and below, the grafts became repeatable and the performanceimproved. The tannin content of the polymer was reduced to 3% tannin.The fluid loss performance was best at that level of tannin.

The molecular weight was modified by holding the temperature constant at70° C. and varying the initiator concentration, acrylamide concentrationand methylenebisacrylamide (MBA) concentration. The acrylamide promotedpolymerization, i.e., the rate and final solution viscosity was higherwhen some acrylamide was added. The acrylamide concentration in theblend of vinyl monomers was varied from 0-18 weight % with the remainderbeing AMPS, i.e., 68-99.95 weight percent. The data in Table 1 belowdemonstrates the effect of various levels of tannin and acrylamide onthickening time. Table 1 sets forth the thickening time results withClass H cement and 1/2% additive.

                  TABLE 1                                                         ______________________________________                                                             THICKENING TIME                                          ADDITIVE             (Minutes)                                                ______________________________________                                        Blank                110                                                      A vinyl polymer with 5% Acam                                                                       153                                                      A vinyl grafted tannin with 3% Tannin                                                              197                                                      and 5% Acam                                                                   A vinyl grafted tannin with 2% Tannin                                                              178                                                      and 10% Acam                                                                  A vinyl grafted tannin with 3% Tannin                                                              217                                                      and 10% Acam                                                                  ______________________________________                                    

The aforementioned data shows that acrylamide and tannin content must bekept relatively low to minimize set time retardation. A crosslinkingagent, e.g., MBA, was added to increase branching and molecular weight.

The vinyl grafted wattle tannin has a weight average molecular weight inthe range between about 90,000 to about 5,000,000.

In the process of forming vinyl grafted wattle tannins according to thepresent invention, a solution of wattle tannin material and either avinyl monomer or a blend of vinyl monomer(s) are charged into a vesselin the presence of an initiator, such as, ammonium persulfate, andheated. This polymerization process grafts the wattle tannin to themonomer(s).

The process for forming an oil well cement composition comprises: mixingcement and a vinyl grafted wattle tannin fluid loss additive, the vinylgrafted wattle tannin comprising a wattle tannin grafted with at leastone vinyl monomer selected from the group consisting of:2-acrylamido-2-methylpropanesulfonic acid and acrylamide, the wattletannin is present in an amount of between about 0.05 to about 14 weightpercent, 2-acrylamido-2-methylpropanesulfonic acid is present in anamount of between about 68 to about 99.95 percent, and acrylamide ispresent in an amount of between about 0 to about 18 percent, to form acement blend; and mixing the cement blend with water.

The vinyl grafted wattle tannin fluid loss additive is preferablyadmixed with dry cement in an amount between about 0.2 to about 2percent by weight of said dry cement. Liquid fluid loss additives areadded to mix water and then a cement slurry is formed by adding drycement to the water/additive mixture under mixing conditions. Driedfluid loss additives are preferably premixed with dry cement and thenadded to the water.

The water used in forming an oil well cement composition is preferablyfresh water, but the water may in some instances contain various salts,such as sodium chloride, potassium chloride, calcium chloride, sea waterand the like.

Other types of well known and conventional additives can also beincorporated into the oil well cement composition in order to modify itsproperties. Such additives may include: additional fluid loss additivesor viscosifiers, retarders, accelerators, dispersants, weight-adjustingmaterials, and fillers. Specific additives are set forth in U.S. Pat.No. 4,676,317 (Fry et al.) which is incorporated herein by reference.

The performance characteristics of the novel vinyl grafted wattle tanninfluid loss additives of the present invention are demonstrated in thetable and examples set forth hereafter. Table 2 below containsperformance data comparing the vinyl grafted wattle tannins (Samples 1,2, and 4) to vinyl grafted lignite (Sample 3) and a non-tannin vinylpolymer (Sample 5).

                  TABLE 2                                                         ______________________________________                                        SAM-  AMPS     Acam                                                           PLE   MOLES    MOLE    MBA   SUBST.                                           NO.   %        %       WT. % WT. %    MW                                      ______________________________________                                        1     90       10      0.4   3% Tannin                                                                              564,000                                 2     100       0      0.1   7% Tannin                                                                              520,000                                 3     90       10      0     20% Lignite                                                                            700,000                                 4     90       10      0     7% Tannin Glutaraldehyde                         5     90       10      0.5   0        1,270,000                               ______________________________________                                                  FWFL     FWFL     FL SALT FL SALT                                   SAMPLE NO.                                                                              (75° C.)                                                                        (180° C.)                                                                       (75° C.)                                                                       (180° C.)                          ______________________________________                                        1         36       46       98       38                                       2         --       60       --      --                                        3         76       118      300+    253                                       4         --       58       --      --                                        5         126      --       300+    --                                        ______________________________________                                    

The fluid loss performance of the vinyl grafted tannin was significantlybetter than the vinyl polymer and vinyl grafted lignite of comparablemolecular weight without tannin. For example, the vinyl grafted tanninof Sample 1 demonstrated fluid loss in fresh water (FWFL) at 75° C. and180° C. of 36/46, respectively; whereas the vinyl grafted lignite ofSample 3 demonstrated fluid loss in fresh water at 75° C. and 180° C. of76/118, respectively. The lower the fluid loss number the better fluidloss performance. Similar fluid loss results were obtained in salt water(FL SALT), i.e., Sample 1 had a fluid loss of 98/38 and Sample 3 was300+/253.

EXAMPLE 1

A vinyl grafted wattle tannin was prepared from the followingcomponents:

    ______________________________________                                        16.10 grams       wattle tannin                                               600.00 grams      water                                                       1.80 grams        50% caustic                                                 0.12 grams        an antifoaming agent                                        606.30 grams      58% Na.sup.+  AMPS                                          24.90 grams       48.6% Acam                                                  1.50 grams        MBA                                                         170.86 grams      water                                                       0.045 grams       ethylenediamine tetracetic                                                    acid, sodium salt (EDTA)                                    75.00 grams       27% ammonium persulfate sodium                                                salt (APS)                                                  3.00 grams        sodium bisulfite (SBS)                                      0.38 grams        biocide                                                     ______________________________________                                    

The aforementioned vinyl grafted wattle tannin was prepared inaccordance with the following grafting procedure. 600 grams of water,16.10 grams of wattle tannin, and 1.80 grams of 50% sodium hydroxidesolution were added to a two liter resin flask. The flask was equippedwith a nitrogen sparge tube, mechanical stirrer, addition funnel,chemical pump feed, condenser, and thermocouple. The pH was 8.5. Thesolution was purged with nitrogen, stirred, and heated to 70° C. A fewdrops of an antifoaming agent were added as necessary to controlfoaming. A solution of 606.3 grams of 58% sodium AMPS, 24.9 grams of 49%acrylamide, 1.50 grams MBA, 170.86 grams of water, and 0.045 grams ofethylenediamine tetracetic acid, sodium salt (EDTA) was pumped steadilyinto the flask over a two hour period. Approximately 3.12 grams of 27%ammonium persulfate (APS) solution was added every 10 minutes, starting10 minutes after the monomer solution feed was begun. The APS solutionwas added over a four hour period. The polymer was reacted 2-3 morehours and 3.00 grams of sodium bisulfite was added. The flask was cooledand the pH was adjusted to about 7. A small amount of a biocide wasadded to control bacterial growth.

The aforementioned vinyl grafted wattle tannin demonstrated a BrookfieldViscosity (BV) of approximately 1550 cp and a pH of 7.0.

EXAMPLE 2

Using the same grafting procedure set forth in Example 1 above, a vinylgrafted wattle tannin was prepared from the following components:

    ______________________________________                                        25.00 grams       wattle tannin                                               4.20 grams        50% caustic                                                 400.90 grams      58% Na.sup.+  AMPS                                          0.25 grams        MBA                                                         511.70 grams      water                                                       0.03 grams        EDTA                                                        58.80 grams       35% ammonium persulfate sodium                                                salt                                                        16.80 grams       hydrochloric acid solution                                  ______________________________________                                    

The aforementioned vinyl grafted wattle tannin demonstrated a BrookfieldViscosity (BV) of approximately 400 cp and a pH of 7.2.

EXAMPLE 3

A tannin resin graft was synthesized from the following components:

    ______________________________________                                        51.50 grams       27.3% active glutaraldehyde                                                   derived tannin resin                                        308.90 grams      58% AMPS                                                    14.40 grams       50% Acam                                                    0.03 grams        EDTA                                                        2.00 grams        50% sodium hydroxide                                        538.00 grams      water                                                       84.00 grams       35% ammonium persulfate sodium                                                salt                                                        18.00 grams       50% sodium hydroxide                                        ______________________________________                                    

The glutaraldehyde derived tannin resin was prepared by reacting 19.7grams of wattle tannin, 1.22 grams of glutaraldehyde, and 30.57 grams ofwater together for five hours at 90° C. and pH 4.3. Water and causticwere added to obtain a pH of 8.5. The monomer solution was fed into theflask for two hours and the initiator was fed into the flask for threehours. This reaction was run at 70° C. After addition of the monomer andinitiator the flask was heated for two hours, then cooled andneutralized. Residual AMPS was <0.1.

EXAMPLE 4

A wattle tannin resin graft was synthesized from the components:

    ______________________________________                                        249.10 grams        a wattle tannin derivative                                                    prepared from 600 grams of                                                    wattle tannin reacted with 40                                                 grams of epichlorohydrin                                  333.30 grams        58% sodium AMPS                                           13.40 grams         49.9% Acam                                                0.03 grams          EDTA                                                      258.40 grams        water                                                     100.00 grams        40% APS                                                   12.00 grams         25% APS                                                   12.00 grams         25% sodium bisulfite                                      ______________________________________                                    

The monomer was fed into the flask for 2 hours and 12 shots of 40% APSinitiator was fed into the flask every 10 minutes at 70° C. Afteraddition of the monomer and initiator the flask was heated, cooled andneutralized. The Brookfield Viscosity of the vinyl grafted tannin was1825 cp. The fluid loss was 14 mL at 1 minute, 33 mL at 4 minutes, 45 mLat 6.5 minutes and 220 mL at 30 minutes.

EXAMPLE 5

A wattle tannin resin graft was synthesized from the followingcomponents:

    ______________________________________                                        328.90 grams          a wattle tannin resin                                   333.30 grams          58% sodium AMPS                                         13.40 grams           49.9% Acam                                              0.75 grams            MBA                                                     0.03 grams            EDTA                                                    223.60 grams          water                                                   100.00 grams          24% APS                                                 12.00 grams           25% APS                                                 12.00 grams           25% sodium bisulfite                                    ______________________________________                                    

The monomer was fed into the flask for 2 hours and 12 shots of 24% APSinitiator was fed into the flask every 10 minutes at 70° C. Afteraddition of the monomer and initiator the flask was heated, cooled andneutralized.

EXAMPLE 6

A quebracho tannin resin graft was synthesized from the followingcomponents:

    ______________________________________                                        249.10 grams       a quebracho tannin derivative                                                 prepared from 600 grams of                                                    quebracho tannin reacted with                                                 40 grams of epichlorohydrin                                333.30 grams       58% sodium AMPS                                            13.40 grams        49.9% Acam                                                 0.75 grams         MBA                                                        0.03 grams         EDTA                                                       294.80 grams       water                                                      100.00 grams       35% APS                                                    12.00 grams        25% APS                                                    12.00 grams        25% sodium bisulfite                                       ______________________________________                                    

The monomer was fed into the flask for two hours and 12 shots of 35% APSinitiator was fed into the flask every 10 minutes at 70° C. Afteraddition of the monomer and initiator the flask was heated, cooled andneutralized. The resultant vinyl grafted quebracho tannin exhibited verypoor viscosity, i.e., BV was 70 cp, and very poor fluid loss properties,i.e., fluid loss of 22 mL at 1 minute, and 41 mL at 2 minutes and 15seconds.

Based upon the above examples it is readily apparent that the vinylgrafted quebracho tannins did not perform nearly as well as the vinylgrafted wattle tannins of the present invention.

EXAMPLES 7-12

Several copolymers of AMPS, acrylamide (Acam) andmethylene-bis-acrylamide (MBA), with and without wattel tannin, wereprepared and tested for fluid loss and molecular weight. The generalprocedure used in preparing these copolymers involved adding a solutionof monomers in water at about pH 8.4 to a 2 liter resin flask. Thesolution was sparged with nitrogen through a condenser and heated toreaction temperature. The temperatures were varied from 44°-48° C. toobtain the desired molecular weight. A 25% aqueous solution of ammoniumpersulfate (APS) was added at reaction temperature to initiate thereaction. The APS solution was varied from 2.00-3.12 grams to obtain thedesired molecular weight. The polymerization was carried out for 21/2 to3 hours to complete the reaction.

Molecular weight for each sample was determined by running it through agel permeation chromatography against sulfonated polystyrene standards.

Fluid loss data was gathered by running the compounds at 0.6% additivebased on weight of dry cement. The slurries contained class H cementwith 38% fresh water. Example 10 was run at 0.6% in class G cement and44% fresh water. Class G fluid loss for Example 10 was 48 ml. The datawere run at room temperature, i.e., 75° F., according to API BulletinSpec. 10.

Table 3 below sets forth the compositional make-up of each of theExamples prepared in accordance with the aforementioned procedures, aswell as the molecular weight and fluid loss of each.

                                      TABLE 3                                     __________________________________________________________________________    No.                                                                              AMPS                                                                              Acam                                                                              MBA TANNIN                                                                              H20                                                                              APS                                                                              EDTA                                                                              MOL. WT (×10.sup.6)                                                               FLUID LOSS (ml)                      __________________________________________________________________________     7 166.7                                                                             6.9 0.35                                                                              0     822.9                                                                            0  0.03                                                                              4.4       162                                   8 166.7                                                                             6.9 0.25                                                                              0     824.1                                                                            2.00                                                                             0.03                                                                              4.9       214                                   9 166.7                                                                             6.9 0.35                                                                              0.05  822.9                                                                            3.12                                                                             0   1.8       94                                   10 166.7                                                                             6.9 0.35                                                                              0.15  822.8                                                                            3.12                                                                             0   1.4       40                                   11 166.7                                                                             6.9 0.35                                                                              0.15  823.4                                                                            2.50                                                                             0.03                                                                              4.0       40                                   12 166.7                                                                             6.9 0.50                                                                              0.15  823.2                                                                            2.50                                                                             0.03                                                                              3.8       38                                   __________________________________________________________________________

While we have shown and described several embodiments in accordance withour invention, it is to be clearly understood that the same aresusceptible to numerous changes and modifications apparent to oneskilled in the art. Therefore, we do not wish to be limited to thedetails shown and described, but intend to show all changes andmodifications which come within the scope of the appended claims.

What is claimed is:
 1. A vinyl grafted wattle tannin fluid loss additivefor use in oil well cement compositions comprising a wattle tanningrafted with at least one vinyl monomer selected from the groupconsisting of: 2-acrylamido-2-methylpropanesulfonic acid and acrylamide,wherein said wattle tannin is present in an amount of between 0.05 to 14weight percent, said 2-acrylamido-2-methylpropanesulfonic acid ispresent in an amount of between 68 to 99.95 percent, and acrylamide ispresent in an amount of between 0 to 18 percent, wherein said vinylgrafted wattle tannin has a weight average molecular weight in the rangebetween 90,000 to 5,000,000.
 2. The fluid loss additive according toclaim 1, where said wattle tannin is a wattle tannin derivative.
 3. Thefluid loss additive according to claim 2, wherein said wattle tannin isderivatized with at least one compound selected from the groupconsisting of:epichlorohydrin, formaldehyde, and glutaraldehyde.
 4. Thefluid loss additive according to claim 1, wherein said vinyl graftedwattle tannin also includes a crosslinking agent.
 5. The fluid lossadditive according to claim 4, wherein said crosslinking agent ismethylenebisacrylamide.
 6. An oil well cement compositioncomprising:cement; water; and a vinyl grafted wattle tannin fluid lossadditive comprising a wattle tannin grafted with at least one vinylmonomer selected from the group consisting of:2-acrylamido-2-methylpropanesulfonic acid and acrylamide, wherein saidwattle tannin is present in an amount of between 0.05 to 14 weightpercent, said 2-acrylamido-2-methylpropanesulfonic acid is present in anamount of between 68 to 99.95 percent, and acrylamide is present in anamount of between 0 to 18 percent, wherein said vinyl grafted wattletannin has a weight average molecular weight in the range between 90,000to 5,000,000.
 7. The cement composition according to claim 6, whereinsaid wattle tannin is a wattle tannin derivative.
 8. The cementcomposition according to claim 7, wherein said wattle tannin isderivatized with at least one compound selected from the groupconsisting of:epichlorohydrin, formaldehyde, and glutaraldehyde.
 9. Thecement composition according to claim 6, wherein said vinyl graftedwattle tannin also includes a crosslinking agent.
 10. The cementcomposition according to claim 9, wherein said crosslinking agent ismethylene bisacrylamide.